This invention relates to dynamoelectric machines having commutators and brushes, and especially to direct current electric motors and generators.
In such machines, the passage of very large currents between the carbon composition brushes and the commutator results in localized heating due to the combination of resistive heating at the contact face and machine commutation. If sufficiently severe, ionization of materials may occur, allowing the creation of an electrical arc with intense heating that will melt materials such as the stainless steel used in the brush holders and copper alloys used in the commutators. It is particularly important, therefore, to prevent the creation of arcing between the portions of the brush holder and the commutator.
In the conventional design of many DC motors, a flange or similar member which is a portion of the brush holder is used to support the junction between the brush pigtail and the stator lead. The brush holder is commonly formed from stainless steel or some other electrically conductive material, and the flange or other portion of the brush holder supporting the junction is similarly constructed of the electrically conductive material.
In such conventional designs, arcing can develop between the commutator and the lower edge of the holder which is in close proximity to the commutator under conditions of especially heavy current through the machine. This arcing results in severe damage to the holders, brushes, and commutator and eventual failure of the machine. For example, the brush holder may be distorted or altered in a way that prevents the spring loaded brush it holds from being urged into full contact with the commutator.